Tensioners for flexible drives, such as accessory serpentine belts on automotive engines are well known. Such tensioners typically include a pulley, roller or other member, which is biased against the flexible drive by a spring or other biasing means. The pulley is mounted, via a bearing, to a tensioner arm which pivots with respect to the tensioner housing. The housing contains the torsion spring, or other biasing means, which biases the arm towards the flexible drive to maintain a substantially constant tension in the flexible drive. Conventional tensioners can also include frictional members which ride on other members as the tensioner arm moves to provide a dampening force to dampen movement of the tensioner arm.
While such prior art tensioners are widely employed, they do suffer from some disadvantages. In particular, due to the relatively large forces which must be carried by the tensioner arm, wear at the pivot that attaches the arm to the tensioner housing is common and such wear can result in the pulley moving to an off-axis position wherein the surface of the pulley is not substantially perpendicular to the engagement surface of the flexible drive. Such off-axis positioning of the pulley results in increased amounts of wear at the pivot and eventually will result in the flexible drive being damaged and/or slipping off the tensioner pulley altogether.
While tensioners with wear compensating means are known, for example from WO 2006/099731 to the present inventors and assigned to the assignee of the present invention, such known tensioners can suffer from being expensive to manufacture and/or assemble.
It is desired to have a tensioner which provides a suitable dampening force, can provide compensation for normal wear of its components and which resists off-perpendicular movement of its components all at a reasonable cost of manufacture.